1. Field of the Invention
The present invention relates to a track counting servo circuit of an optical disk apparatus, and more particularly, to a track counting servo circuit that compensates for track counting errors to permit accessing the disk at high speeds.
Korean Patent Application No. 93-9360 is incorporated herein by reference for all purposes.
2. Discussion of Related Art
In general, a variety of deviations occurring in an optical disk apparatus such as CD-ROMs, compact disk graphics (CDG) players and compact disk players (CDPs) are compensated by a plurality of servo apparatus. Examples of these servos include a focusing servo, a tracking servo, a constant line velocity (CLV) servo, a feeding servo, etc. The focusing servo is used to compensate by detecting the amount of up-and-down (longitudinal) fluctuation on the track due to the rotation of the disk. The tracking servo is used to compensate by detecting the amount of left-and-right (latitudinal) fluctuation on the track, which is also due to the rotation of the disk. Further, the CLV servo is used to compensate the time value of the data according to the rotational fluctuation of the disk. Also, two methods are classified depending on how the beam spot of the optical disk apparatus is moved. One method is a track jumping method for moving an objective lens, and the other is a sled method for moving the pickup itself. Accordingly, a microscopic tracking servo is used for tracing on the track of a compact disk using the objective lens movement, and a sled servo is used for tracing on the track using the movement of the pickup itself.
In a CD-ROM, the speed at which information is read from the disk determines the quality of the product. This is different from that of a CDG or CDP, where the motor should be accurately controlled in the pickup transportation, track jump and track transportation by means of the sled motor, in order to minimize access time.
FIG. 1 is a block diagram of the conventional servo control circuit. Referring to FIG. 1, the servo control circuit comprises a disk 11; a pickup 12 for reading out the data from disk 11; a radio frequency (RF) amplifier 13 for amplifying the track counting signal detected by pickup 12 when counting the track number; a counter 14 for counting the number of tracks; and a microcomputer 15 for controlling the tracking servo.
Referring to the operation of the servo control circuit having the structure as shown in FIG. 1, microcomputer 15 calculates the number of tracks from a given point to the target track and drives the sled motor, to thereby transport the pickup 12 across as many tracks as calculated. RF amplifier 13 amplifies and outputs the RF signal representing the track being input by means of the moving pickup 12 following the instruction of microcomputer 15. Counter 14 counts the number of tracks being currently input, and if the number is equal to the number of tracks calculated by microcomputer 15, microcomputer 15 produces an instruction to halt the sled motor, so that pickup 12 will stop on the target track.
The conventional movement of the pickup according to the above-described method creates a situation in which the pickup cannot count the tracks for a predetermined duration due to limitations of the signal read frequency and the external impact when the sled is driven at high speeds, and thus the pickup may move beyond the target track by as many tracks as not counted, which becomes a serious problem for high speed access.